The present invention relates to a compliant link and in particular a compliant link for a gear engagement mechanism and more particularly, a gear engagement mechanism for a multi-ratio gearbox used in an automated transmission system.
In automated transmission systems, for example automated manual transmission systems or for automatic or semi-automatic transmissions including a multi-ratio gearbox of, for example, the type disclosed in WO97/05410 or WO97/40300, whose content is expressly incorporated in the disclosure content of the present application, a gear engagement mechanism comprises a plurality of shift rails, each shift rail being associated with two gear ratios of the gearbox, via a selector fork and synchromesh unit, so that axial movement of each shift rail in either direction will engage one of the associated gear ratios.
A selector member is moved by a select actuator in a select direction transverse to the shift rails, to be indexed with and engage a selected one of the shift rails and, by a shift actuator, in a shift direction, axially of the shift rails, to move the selected shift rail axially in one direction or the other, to engage the selected gear ratio.
Alternatively, as disclosed in for example UK patent application GB0028310.1, whose content is expressly incorporated in the disclosure content of the present application, each shift rail may be provided with a separate shift actuator, the shift actuator being connected directly to the shift rail for movement of the shift rail axially in either direction.
In accordance with WO97/05410, WO97/40300 and GB0028310.1, the select and shift actuators are hydraulic actuators. DE19734023, whose content is expressly incorporated in the disclosure content of the present application, discloses the use of electric motors to move the selector member in the first and second directions respectively.
With hydraulic actuation systems, it is desirable to have low compliance in the hydraulic system and, due to the high dynamic potential of such systems, it is necessary to decelerate the hydraulic shift actuator considerably, before hitting the synchroniser. Without a cautious control of the shift actuator, a high pressure peak can be generated at the start of synchronisation, which can lead to hardware damage and reduces the driving comfort, causing noise and jerks in the drive line.
The present invention provides a compliant link which may be located between the shift actuator and the shift rail, which will limit the initial load which will be applied to the synchroniser, thereby avoiding damage thereto and reducing noise and jerks in the drive line.
According to one aspect of the present invention, a compliant link comprises first and second members, said members being interconnected by resilient means, the resilient means being preloaded to prevent relative movement between the members when an axial load below a first predetermined value is applied to one of the members.
According to a preferred embodiment of the invention, the link is a double acting link providing for compliance for axial movement of the link in either direction.
According to a further preferred embodiment, relative movement between the members is limited, so that relative movement will not occur between the members when an axial load above a second predetermined value is applied to one of the members.
A compliant link described above may be located between the shift actuator and a shift rail of the transmission system, whereby the initial loads applied to a synchromesh unit associated with the shift rail may be moderated, thereby avoiding damage to the synchromesh unit and noise and jerks etc. in the drive line.